Overview of BFD

This section describes the definition and purpose of BFD.

Definition

Bidirectional Forwarding Detection (BFD) quickly detects communications faults between systems and reports corresponding faults to the upper-layer protocol.

Objective

To minimize the impact of failures and improve network availability, network devices need to rapidly detect communication failures to take early remedial actions to ensure service continuity.

The current fault detection mechanisms include:

Hardware detection: For example, the Synchronous Digital Hierarchy (SDH) alarms are used to detect faults on links. This mechanism features quick identification of faults; however, not all medium can provide this mechanism.
Slow Hello mechanism: It usually refers to the Hello mechanism offered by a routing protocol. The slow Hello mechanism can detect a fault in seconds. In high-speed data transmission, for example, at Gbit/s rate, the detection delay of more than one second causes the loss of a large amount of data. In delay-sensitive services such as the voice service, the delay of more than one second is unacceptable.
Other detection mechanisms: Specific detection mechanisms may be provided by different protocols or device vendors. If a network has devices from multiple vendors, these detection mechanisms are difficult to implement.

BFD overcomes the limitations of earlier detection mechanisms.

BFD provides the following functions:

Provides low-overhead and quick fault detection for channels between adjacent forwarding engines. The detected faults may occur on interfaces, data links, or forwarding engines.
Provides a single mechanism to detect any media and protocol layers in real time. In addition, the detection duration and overhead range are variable.